When is it said that "an" is estimated as obligatory or permissible?

The questioner : Shaykh, why do you say obligatory or permissible?

The Shaykh : Ah?

The questioner : Saying obligatory means it is considered... permissible.

The Shaykh : This is according to the opinion of the Basrans. Permissible is that in which it is permissible for "an" to appear, and obligatory is that in which "an" does not appear. For example, in , "an" does not appear; you do not say "It was not for Allah to punish them because..." But in "I came to read," it is permissible for "an" to appear, so you say "I came to read." This is according to the opinion of the Basrans. As for the opinion of the author, he says that all of them are in the accusative case. There is no need to say "on the estimation of 'an,'" neither permissible nor obligatory. And this is a feature of following the easier path. Yes.